It is known by the Applicant's previous work to print a conductor layer over a flexible substrate, followed by printing a monolayer of microscopic vertical LEDs over the conductor layer in the desired orientation so that bottom electrodes of the LEDs ohmically contact the conductor layer. A dielectric layer is then printed over the conductor layer, followed by printing a transparent conductor layer to contact the top electrodes of the LEDs and connect the LEDs in parallel. A layer of phosphor may be optionally printed over the LEDs to wavelength-convert the LED light. When a sufficient voltage is applied to the conductor layers, the LEDs emit light through the transparent conductor layer. Further detail of forming a light source by printing microscopic vertical LEDs, and controlling their orientation on a substrate, can be found in US application publication US 2012/0164796, entitled, Method of Manufacturing a Printable Composition of Liquid or Gel Suspension of Diodes, assigned to the present assignee and incorporated herein by reference.
The thickness of the substrate may exceed 250 microns. The thickness of the combined LED/conductors layers may be as thin as 20 microns. If the phosphor layer were included, the thickness of the LED/conductor/phosphor layers may be around 60 microns.
The resulting LED lamp is flexible to a certain radius. However, the flexibility is limited by the substrate, which is more rigid than the LED/conductor layers, and stresses created by the different radii of the substrate and LED/conductor layers when bending could stretch or tear the LED/conductor layers, possibly destroying the lamp. Further, in some applications of the lamp, such as for laminating the lamp to an article of clothing, the substrate causes the lamp to be much stiffer than the clothing and causes the overall thickness of the lamp to be problematic.
Additionally, since the substrate remains on the final LED lamp product, the substrate should be optimized for the final product rather than optimized for the manufacturing process, such as a roll-to roll process. Therefore, there is a trade-off between optimizing manufacturability and optimizing the final product. The substrate also adds cost to the final product.
What is needed is a technique for forming a printed LED lamp that does not suffer from the issues described above relating to the substrate.